1. Technical Field
This invention relates to the art of producing composite welded components joined together from at least two metal workpieces, which workpieces must be surface hardened.
2. Description of the Prior Art
In the production of composite welded components, the practice has been to first mechanically finish each of the two workpieces, separately, and then heat treat each of the workpieces, also separately, to harden their surface. The carbonization of the surface (which occurs during the heat treatment to improve the properties of the material) will extend over the contact surfaces of the workpieces, which contact surfaces must be brought together for welding. If welding is carried out with electron beams, to promote fusion and vaporization of the metal, it is necessary to remove the carbonized layer on the contact surfaces of the workpieces before such welding. The hardened workpieces must therefore be machined in a sub-step of the preceding finishing process, or in a correspondingly separate finishing process for additional individual machining, in order that the contact surfaces may have a welding zone that permits satisfactory welding. For welding carried out by means of laser beams, layers of this type (ones which are carbonized during a preceding heat treatment of the workpieces) must also be removed from the welding zone, again beforehand. In the case of manufacturing composite gearwheels, for example, which are required for vehicle transmissions, this undesirably necessitates extra time and high cost.
German Pat. No. DE-PS 2920719 discloses a method which attempts to inhibit hardening during heat treatment of a welding zone, but does so in a manner that is cumbersome, costly, and does not insure close tolerances of the workpieces after heat treatment. This German patent requires use of covers and blocks for maintaining the inner bore of a gear free of hardening to facilitate welding. The extra handling and use of blocks prevents simplification and reduction of costs, and does little to inhibit distortion of the parts during heat treatment.